Grain sorghum is a grain commodity that gets overshadowed by corn, soybean, and wheat. Most people don’t realize that this commodity is widely grown in certain areas of the United States and contributes to U.S. farming income. A factor with the potential to reduce grain sorghum yields and profitability is sorghum foliar disease(s). To help maintain yield potential, grain sorghum fields should be scouted for developing foliar diseases and managed accordingly.
Most sorghum leaf diseases are caused by bacteria or fungi; however, viruses can also be a cause. Common foliar diseases are bacterial stripe, bacterial streak, bacterial spot, northern corn leaf blight, zonate leaf spot, and grey leaf spot. The diseases are spread by wind born particles, contaminated plant debris from the previous crop, and insect pressure.
Bacterial diseases generally survive from season to season in seed and on crop residue. The diseases are spread by wind, splashing rain, and insects. They are most severe during warm (75 to 80° F), moist growing conditions.1
Bacterial stripe is characterized by long, narrow, red stripes which initially appear on the lower leaves. The stripes tend to appear between the veins and generally range in length from ¼ inch to greater than nine inches.1
Bacterial streak appears as very narrow stripes which are one to six inches long. The lesions can develop anytime during the plant’s life; however, they usually appear on the lower leaves initially. Red-brown blotches develop within the streaks, which can enlarge into oval spots with tan centers and narrow, red margins.1
Bacterial spot lesions are small, irregular, and tan with dark margins.
Common fungal diseases of sorghum include anthracnose, northern corn leaf blight, target spot, gray leaf spot, zonate leaf spot, and rust.1
Anthracnose appears as small, elliptical to circular lesions with straw-colored centers with margins that vary from reddish to tan to blackish purple (Figure 1).2 The peduncle holding the sorghum head can also be infected.2
Leaf blight or northern corn leaf blight is characterized by irregular long (one inch or more) gray lesions with tan-red borders.
Target spot has round, elliptical tan spots (1/8 inch to one inch wide) that have red borders.
Gray leaf spot, which is common in corn, has elongate (1/4 inch or more) to rounded lesions that are initially dark purple and become grayish as the lesions mature.
Zonate leaf spot is characterized by a bull’s eye appearance with circular lesions that are ¼ to 2 inches wide (Figure 2). The lesions have alternating bands of dark purple and tan.
Rust on sorghum appears as round to elliptical, small raised pustules which are light red-brown and usually develop on the oldest leaves.
A viral disease that can develop in fields with Johnsongrass is Maize dwarf mosaic virus (MDMV). The disease is spread when corn leaf aphids and greenbugs feed upon infected Johnsongrass shoots and then move to grain sorghum. Infected leaves have distinctive mottling and are yellow with light green islands.1 Infected leaves may turn red when temperatures are below 55° F. Afterwards, elongated tan stripes with red margins develop. Infected plants may be stunted without a normal head and usually die.1
Management practices to help mitigate the risk of disease development can include:
- Crop rotation: By planting a crop that doesn’t become infected by a grain sorghum disease, the potential for pathogen survival is reduced.
- Plant grain sorghum tolerant products: Scout your fields so you understand the foliar disease and pressure that you are seeing. This way you can make future product selections that have resistance or tolerance to some of these diseases.
- Fungicides: Check with your local retailer to determine if a fungicide would be beneficial for protecting potential yield. It is important to understand that fungicides do not manage bacterial or viral diseases.
There are ideal weather conditions that make these diseases move quicker than others and no two years are the same. It is always a great practice to make sure you are scouting your fields throughout the growing season. This can help you make the best management decisions for your growing crop and help maximize yield potential.
1Wrather, A. and Sweets, L. 2009. Management of grain sorghum diseases in Missouri. University of Missouri. https://extension.missouri.edu/g4356#Diseases.
2Grain sorghum disease. Texas A&M Agrilife Research and Extension Center at San Angelo. Texas A&M University. https://sanangelo.tamu.edu/extension/agronomy/agronomy-publications/grain-sorghum-production-in-west-central-texas/grain-sorghum-disease/.
ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Performance may vary, from location to location and from year to year, as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on the grower’s fields.
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